Noise, particularly blade passing tone, produced by an axial flow fan of an engine cooling system has been a concern in the automotive industry. The term "axial flow fan" used herein refers to any fan of the general type in which the flow of air or other gas is in a direction parallel to the axis about which the fan blades rotate.
A technique for reducing noise in axial flow fans includes employing noise absorption material in regions near the fan or otherwise adjacent to the fluid flow. This technique is helpful but the effectiveness is limited in certain frequency ranges such as absorbing the passing blade tonal frequency.
Accordingly, there is a need to provide a cooling structure including at least one resonator thereon so as to reduce or eliminate blade passing tonal noise.